Experimental assessment of stress patterns in abdominal aortic aneurysms using the photoelastic method

Abdominal aortic aneurysm (AAA) sac size is a major clinical problem. The maximum sac diameter is the major determining factor for treatment. There is a direct correlation between the wall stress and rupture sites for AAA with maximum wall stress not being dependent on the maximum diameter of the vessel but on the morphology of vessel. The reflective photoelastic method was developed to experimentally evaluate the stresses and strains in a model AAA. The epoxy resin material was used as the self-supporting structure and had similar mechanical properties to the aneurysmal aorta. For both static and dynamic fluid testing the high-stressed regions were located proximally and distally to the aneurysm. This correlates to reported in vivo rupture sites. There was a low-stress region at the location of greatest diameter at the centre of the aneurysm. The direction of the maximum principal stress was found to be in the circumferential direction. The maximum stress for a high blood pressure of 22.7 kPa (170 mmHg) was 35% greater than that for a normal blood pressure of 16.0 kPa (120 mmHg). The photoelastic method is a powerful and innovative method of analysing stresses in AAA models, producing results, which are visual and easy to interpret.